Radio Frequency IDentification (RFID) systems typically include RFID tags and RFID readers (the former are also known as labels or inlays, and the latter are also known as RFID reader/writers or RFID interrogators). RFID systems can be used in many ways for locating and identifying objects to which the tags are attached. RFID systems are particularly useful in product-related and service-related industries for tracking large numbers of objects being processed, inventoried, or handled. In such cases, an RFID tag is usually attached to an individual item, or to its package.
In principle, RFID techniques entail using an RFID reader to interrogate one or more RFID tags. The reader transmitting a Radio Frequency (RF) wave performs the interrogation. A tag that senses the interrogating RF wave responds by transmitting back another RF wave. The tag generates the transmitted-back RF wave either originally, or by reflecting back a portion of the interrogating RF wave, in a process known as backscatter. Backscatter may take place in a number of ways.
The reflected-back RF wave may further encode data stored internally in the tag, such as a number. The response is demodulated and decoded by the reader, which thereby identifies, counts, or otherwise interacts with the associated item. The decoded data can denote a serial number, a price, a date, a destination, other attribute(s), any combination of attributes, and so on.
An RFID tag typically includes an antenna system, a power management section, a radio section, and frequently a logical section, a memory, or both. In earlier RFID tags, the power management section included a power storage device, such as a battery. RFID tags with a power storage device are known as active tags. Advances in semiconductor technology have miniaturized the electronics so much that an RFID tag can be powered solely by the RF signal it receives. Such RFID tags do not include a power storage device, and are called passive tags.
The tag can control the periodicity of the symbols it backscatters. In other words, it can control the basic backscatter period it uses, along with the encoding scheme. In a number of embodiments, the reader transmits an instruction about the periodicity, and the tag follows the instruction. In some instances, the instruction as it pertains to the basic backscatter period calls for a division by a non-integer, which the tag can follow by implementing cumbersome circuitry, with concomitant penalties in die area, chip power, and eventual chip performance and cost.